New Dinosaur Finds Show Long, Slow Die-off

November 10, 1986|By KNT News Service

PHILADELPHIA — Dinosaurs did not become extinct when a giant asteroid or comet slammed into Earth 65 million years ago, a theory that has gained wide popularity in recent years, according to new evidence.

''Our findings show that the dinosaurs went out not with a bang but a whimper,'' said Robert Sloan, of the University of Minnesota, who presented his findings during the weekend at a national scientific meeting held at the Academy of Natural Sciences.

Sloan and Keith Rigby, of the University of Notre Dame, reported having found evidence in China and Montana of dinosaurs that lived up to 750,000 years after an asteroid crashed into Earth, more recently than any other dinosaur evidence ever found.

''The implications of our findings are monumental,'' said Rigby, a professor of earth sciences. ''At the minimum, they show an asteroid did not cause the extinction of the dinosaurs.''

The professors said they believe dinosaurs gradually died out for a number of reasons during a period of 7 million years.

While the scientists do not dispute that an asteroid crashed, raising clouds of dust that enveloped Earth, they rebut the theory that the crash ended the 160-million-year reign of dinosaurs.

In 1980, physicist Luis Alvarez and his son Walter, a geologist, first proposed that an asteroid 6 miles wide hit Earth at 40,000 mph, setting off a blast 1,000 times greater than if the world's entire nuclear arsenal exploded. The father-son team said the crash sent up so much dust and soot that sunlight was blocked and temperatures fell. As a result, plants withered, animals starved or froze to death and the dinosaurs went extinct -- enabling mammals to dominate Earth.

Sloan and Rigby said many factors probably conspired to kill off the dinosaurs, including a 30-degree drop in global temperatures during this period, which caused the dinosaurs' habitat to shift from a tropical to a temperate climate.

They pointed to fossil evidence that more than half of the species of plants found in Montana died off during 3 million years, drastically altering the dinosaurs' food supply.

Also, changes in the oceans' sea floor caused the global sea level to drop 1,000 feet during this period, causing land bridges to form between Asia and North America. This enabled mammals to migrate into the dinosaurs' habitats, increasing competition for food, they said.

''The changes affected the dinosaurs far more than the smaller mammals,'' said Sloan, a professor of geology and geophysics. ''There was a plague of mammals. The dinosaurs were squeezed in every conceivable way.''